NGWS SDK Documentation  

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Compiler Warning (level 1) C4540

dynamic_cast used to convert to inaccessible or ambiguous base; run-time test will fail ('type1' to 'type2')

You used dynamic_cast to convert from one type to another. The compiler determined that the cast would always fail (return NULL) because a base class is inaccessible (private, for instance) or ambiguous (appears more than once in the class hierarchy, for instance).

The following shows an example of this warning. Class D is derived from class B. The program uses dynamic_cast to cast from class D (the derived class) to class B, which will always fail because class B is private and thus inaccessible. Changing the access on B to public will fix the problem.

class B { virtual void g(); };
class D : private B {};

void a() {
   D   d;
   B*   bp;
   bp = dynamic_cast<B*>(&d); // error C4540
}